Christine Kenneally in the New York Times:
Faced with pictures of odd clay creatures sporting prominent heads and pointy limbs, students at Carnegie Mellon were asked to identify which “aliens” were friendly and which were not.
The students were not told that the aliens fell naturally into two groups, although the differences were subtle and not easy to describe.
Some had somewhat lumpy, misshapen heads. Others had smoother domes. After students assigned each alien to a category, they were told whether they had guessed right or wrong, learning as they went that smooth heads were friendly and lumpy heads were not.
The experimenter, Dr. Gary Lupyan, who is now doing postdoctoral research at Cornell, added a little item of information to one test group. He told the group that previous subjects had found it helpful to label the aliens, calling the friendly ones “leebish” and the unfriendly ones “grecious,” or vice versa.
When the participants found out whether their choice was right or wrong, they were also shown the appropriate label. All the participants eventually learned the difference between the aliens, but the group using labels learned much faster. Naming, Dr. Lupyan concluded, helps to create mental categories.
More here.